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In recent weeks, multiple aides have been interviewed -- some more than once, officials said

(CNN)Some of Hillary Clinton's closest aides, including her longtime adviser Huma Abedin, have provided interviews to federal investigators, as the FBI probe into the security of her private email server nears completion, U.S. officials briefed on the investigation tell CNN. The investigation is still ongoing, but so far investigators haven't found evidence to prove that Clinton willfully violated the law the U.S. officials say.

In recent weeks, multiple aides have been interviewed -- some more than once, the officials said. A date for an FBI interview of Clinton has not been set, these officials said, but is expected in the coming weeks. Abedin has cooperated with the probe, the officials said. Lawyers for Abedin declined to comment. The officials say the interviews of Clinton and her aides would be a routine part of an investigation like this.

The Clinton campaign said Thursday that they've cooperated with the Justice Department review since the beginning.

"From the start, Hillary Clinton has offered to answer any questions that would help the Justice Department complete its review, and we hope and expect that anyone else who is asked would do the same. We are confident the review will conclude that nothing inappropriate took place," Clinton's press secretary Brian Fallon said in a statement.

The probe remains focused on the security of the server and the handling of classified information and hasn't expanded to other matters, the officials said. Spokesmen for the FBI and Justice Department declined to comment. David Kendall, an attorney for Clinton, had no comment.

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CNN has previously reported that another former Clinton employee, Bryan Pagliano, who helped set up the server has provided documents and other materials as well as interviews to the FBI, under an immunity agreement. FBI officials overseeing the probe now expect to complete their work in the next few weeks and then turn over the findings to the Justice Department, which will make a final decision on whether to bring charges against anyone. Prosecutors from the Justice Department's national security division and from the U.S. Attorney's office in Alexandria, Va., have helped coordinate the FBI probe, closely overseeing investigative steps, the U.S. officials say.

One of the final and most anticipated steps in the probe is an interview of the former secretary of state. The fact that Clinton is a presidential candidate active on the campaign trail presents some logistical challenges for the FBI, which has been quietly bringing witnesses into an FBI office without drawing attention.

Clinton's security is provided by the Secret Service and she's typically followed by a corps of campaign reporters. The FBI plans to coordinate her interview with her attorneys and security to try to ensure it can be done privately.

In addition, this week, a notorious hacker awaiting trial claimed he infiltrated Clinton's server but law enforcement officials said the FBI investigation into Guccifer found no sign he got into the Clinton server according to law enforcement sources.